Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $220.58   11.365%   $245.6489   $245.65   $245.65   $245.60  
  Purchase #2 $88.51   10.272%   $97.6017   $97.60   $97.60   $97.60  
  Purchase #3 $117.96   12.608%   $132.8324   $132.83   $132.85   $132.80  
  Purchase #4 $247.63   4.347%   $258.3945   $258.39   $258.40   $258.40  
  Purchase #5 $49.99   5.532%   $52.7554   $52.76   $52.75   $52.80  
  Purchase #6 $202.47   3.658%   $209.8764   $209.88   $209.90   $209.90  
  Purchase #7 $44.59   4.132%   $46.4325   $46.43   $46.45   $46.40  
  7 purchase totals = $971.73       $1,043.5418   $1,043.54   $1,043.60   $1,043.50